1. Field of the Invention
The present invention relates to projection-type image display devices, and more particularly, to a projection-type image display device provided with a scintillation-reducing function.
2. Description of the Related Art
In projection-type image display devices, such as rear-projection televisions, lamps or laser oscillators are used as light sources. When a laser oscillator is used as the light source, it is comparatively straightforward to realize a projection-type image display device with a brightness high enough to allow clear images to be displayed even in bright rooms. However, when a laser oscillator is used as the light source, so-called scintillation, a screen glare phenomenon due to a speckle pattern, becomes noticeable as compared with displays in which lamps are used as the light sources.
Conventional methods of reducing the scintillation involve vibrating the screen in a direction perpendicular to the image display surface of the screen, in the longitudinal direction of the screen, or in the lateral direction of the screen, or alternatively, vibrating the laser beam on the screen in a direction at right angles to the optical axis as disclosed, for example, in Japanese Patent Application Laid-open No. S55-65940. The screen is vibrated in the directions described above with a vibrating device that includes a bimorph, motor, or the like, and the laser beam is vibrated in the direction described above by reflecting the laser beam towards the screen with a vibrating mirror attached to a vibrating device or by deflecting the laser beam in front of the screen with a deflecting device attached to a vibrating device, or alternatively, by vibrating the laser light source itself.
However, when the screen is vibrated in a direction perpendicular to the image display surface of the screen (the normal direction), image jitter occurs and the resolution is reduced, thus reducing the image quality as a result. Moreover, when the screen is vibrated in the longitudinal direction or the lateral direction thereof, the screen momentarily stops at the positions of maximum displacement from the origin where the oscillating direction reverses, thus producing strong scintillation at those points. The same also applies when vibrating the laser beam in directions at right angles to the optical axis.